(1) Field of the Invention
The present invention relates to a transfer mechanism and an image forming apparatus using the same, and in particular, relates to a transfer mechanism which is used in an image forming apparatus that is applied to a copier, multi-functional machine, printer, facsimile machine and the like that uses electrophotography and outputs images in accordance with print requests, as well as to an image forming apparatus using this transfer mechanism.
(2) Description of the Prior Art
A typical transfer mechanism for use in an image forming apparatus has a function of transferring image information (toner image or developer image) that was developed on an electrostatic latent image support (photoreceptor drum), to a recording medium (paper) being conveyed, by bringing the paper into contact with the photoreceptor drum while applying a transfer electric field to the paper from the rear side of the paper.
In recent years, with the trend of image forming apparatus towards becoming compact and high-speed in configurations, use of a belt transfer system using an endless belt as a transfer mechanism has been increasingly developed.
The belt transfer system is constructed such that an endless belt is used to convey the paper while the paper or the endless belt is brought into contact with a photoreceptor drum to thereby transfer the toner image visualized on photoreceptor drum to the paper or endless belt. In most cases, the belt transfer system is provided in the form that includes a belt contact and separation mechanism for moving the endless belt into and out of contact with the photoreceptor drum.
Actually, during the transfer stage, the paper or the endless belt is brought into contact with the photoreceptor drum, but during the non-transfer stage, the belt needs to be kept out of contact with the photoreceptor drum so as to prevent the endless belt from being worn out or deteriorated.
To deal with this, there has been a known technique, as a conventional belt contact and separation mechanism, which uses a cam mechanism to move the transfer unit relative to the photoreceptor drum (see patent document 1: Japanese Patent Application Laid-open H08-137166). Illustratively, an endless belt (transfer belt), a multiple number of rollers that support the belt and a transfer roller are assembled as a single transfer unit, and this transfer unit as a whole is moved into and out of contact with the photoreceptor drum by a cam system.
However, since the above cam mechanism is configured to be driven by actuating cams by manually rotating a handle, it needs a complicated drive coupling technique. Further, since the transfer unit is manually moved up and down, there is the problem of poor response when it is applied to a high-speed printing process.
To avoid this problem there is a method of moving the transfer unit as a whole by using, as a drive source, a solenoid which presents excellent operational response. In this case, a multiple number of cams are arranged in series along the width direction of the transfer belt, and the multiple cams coupled in series are operated by switching on and off a single solenoid.
However, in the above method using a solenoid, there occur some cases in which contact and separation between the transfer belt and the photoreceptor drum cannot be achieved smoothly due to an operational delay of the cam or cams located on the far side from the solenoid depending on the assembly and/or machining accuracy. For example, there occurs a case in which the transfer belt comes into contact with the photoreceptor drum on the side near to the solenoid while it remains away from the photoreceptor drum on the side far from the solenoid.